Reverse DNS Lookup.
Find the hostname set for an IP address (its PTR record) and check that the name points back to the same address. Mail servers run this exact test.
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What Is a Reverse DNS Lookup?
Normal DNS turns a name into an IP address. Reverse DNS does the opposite: it turns an IP address back into a hostname, using a PTR record stored under a special name ending in in-addr.arpa for IPv4 or ip6.arpa for IPv6.
The PTR record is set by whoever controls the IP address, usually the hosting company or internet provider, not by the owner of the domain. Mail servers read it to judge senders: a mail server whose IP has no reverse DNS, or whose reverse name does not point back to the same IP, is far more likely to be treated as spam.
This tool shows the PTR hostname and then looks that hostname up again, so you can see if the two match. To see who owns the address, use the IP address lookup.
What the Address Says About Itself.
The tool asks DNS for the PTR record, then looks the hostname up again to see whether it leads back to the same IP address.
PTR hostname
The name the owner of the IP address has set for it, such as dns.google or mail.example.com.
Forward-confirmed check
Whether the hostname resolves back to the same IP. This is called forward-confirmed reverse DNS (FCrDNS).
Email reputation
Mail servers distrust senders with no PTR or a mismatch. A matching pair is one of the first checks they run.
IPv4 and IPv6
Both address types work. The tool builds the in-addr.arpa or ip6.arpa name for you.
Common Problems and Fixes.
Reverse DNS problems usually show up as email that is rejected or sent to spam.
No PTR record is set
Ask your hosting provider to set reverse DNS for your IP. On most VPS control panels this is a field next to the IP address. Use your mail server's hostname.
The hostname does not point back to the IP
Add an A record (or AAAA for IPv6) for the PTR hostname that points to the same IP, so the pair matches.
The PTR looks generic
Names such as 203-0-113-5.provider.net are set by the provider and are treated as home or dynamic addresses by some mail servers. Set a proper mail hostname.
Several PTR records exist
Keep one PTR record per IP address. More than one can confuse mail servers.
Mail still goes to spam after fixing it
Reverse DNS is one check of several. Also check SPF, DKIM and DMARC with the email authentication checker, and the IP with the blacklist check.
I cannot change the PTR record
Only the owner of the IP block can. If you rent the IP, open a ticket with the provider and name the hostname you want.
Related Free Tools.
Frequently Asked Questions
Quick answers about this tool.
Send Email from Your Own Server?
KVM VPS with full root access and a dedicated IPv4 address. Ask us to set reverse DNS to your mail hostname.